Willett, 28, who won his first major last month, sank six birdies in a bogey-free round to trail YE Yang, Joost Luiten and Scott Hend.
"It's always nice to play in front of home crowds. The reception on the first tee was amazing," said Willett.
Fellow Englishman Robert Rock is five under; Luke Donald is one further back.
Former world number one Donald, who beat Lee Westwood in a play-off at Wentworth in 2011 and successfully defended the title 12 months later, said: "I love getting off to a good start on Thursdays, that seems to be the key for me. That was a perfect start for me.
"The last year or two has been tough, I've struggled to gain confidence and feel comfortable but the last couple of months I'm feeling more and more comfortable and it's nice to see some better results. I feel like I am on the upward path."
Willett finished 11 shots behind winner Rory McIlroy at the Irish Open last week and says he wants the same support the four-time major winner got in his home event.
